I have sound working great with alsa right now on my debian box, but every time I log in, or start certain applications (haven't really found the pattern here yet, but I think kmplayer using xine does it), my sound volume gets really quiet, and there's tons of line noise. This is also how my sound behaved before installing alsa, just all the time. Running alsaconf restores my sound to being awesome, but I'd just like it to be awesome all the time. I realize there's not much to go on here, but I'm willing to answer any other questions anyone has.

You may need to run 'alsactl store' as root, but you seem to be describing it booting properly and going nuts mid-session, right? So, yeah, xine screws with the volume, at least in some cases. I don't know what would cause the noise though. You can try editing ~/.xine/config and putting
in there. I don't think that's the correct way, but it was all I could do to beat xine into submission. May help you.

-- On second thought, another possibility is that it may be a problem of xine trying to use OSS or the OSS wrapper rather than alsa directly. Xine may have an option to specify that, but I don't have it installed at the moment, so I dunno. May give you something to search the web for, anyway.

Hmm, yes, to make the comparison to my system (Slackware, what's yours? Actual 'Debian?) mine uses init scripts. I'm quite unfamiliar with Debian, so excuse me if I'm out in left field here
Upon bootup/ login, the init scripts run 'alsactl -restore' which reloads the previously saved alsa settings. The exact script is /etc/rc.d/rc.alsa .
Before shutdown (or sometime like that) the system does an 'alsactl store' to save the current settings.
So, after you go and to 'alsaconf' as root, and get it all working, do 'alsactl store' to save it.
Then, if it doesn't already exist somewhere, create a script or add a line to an existing one like rc.local, which reloads the alsa settings upon reboot.
This is just the basics of the alsa settings. If you are actually having an issue where a particular application is screwing up the alsa settings, I'm not sure what to suggest. Need some more detail, as you learn what's actually happening there..

As long as you have the alsa-utils package, Debian runs alsactl from /etc/init.d/alsa-utils, which is symlinked to items in rc{0,6,S}.d. (Debian uses the lame sysv-init style init scripts.) It should take care of the store and restore, so that was just an obligatory mention.